This invention relates generally to an axial piston motor that utilizes a swash plate construction, in particular a wheel motor, with a stationary support part that contains a swash plate and a control surface and a rotating output part into which a cylinder drum is integrated. Common bearings are present for mounting the cylinder drum and the support part.
An axial piston motor of the type described above, in which the cylinder drum acts directly as the output part without the interposition of an output shaft (and which is why such an axial piston motor can also be called xe2x80x9cshaftlessxe2x80x9d), is described in DE 196 42 022 A1, which is herein incorporated by reference. This known axial piston motor consists of only a small number of individual parts. On the known axial piston motor, the wheel loads are introduced into the stationary support part by means of a stud axle. The wheel loads determine the diameter of the stud axle and thus the minimum dimensions of the cylinder drum and of the axial piston motor in the radial direction.
An object of this invention is to provide an axial piston motor of the type defined above, the cylinder drum of which can be configured with smaller radial dimensions.
The invention teaches that bearings are located radially between a cylinder drum and a bearing bush that is connected with a support part and surrounds the cylinder drum. A teaching of the invention is consequently to provide an external arrangement of bearings of the cylinder drum in a bearing bush. Such a layout makes it possible to reduce the dimensions of the cylinder drum and of the axial piston motor in the radial direction, as a result of which the weight of the cylinder drum and of the entire drive system can be significantly reduced. An axial piston motor in accordance with the invention therefore has higher dynamic characteristics than the known axial piston motor described above, and can be operated at higher speeds. As a result of the reduced dimensions, the manufacturing costs can also be reduced. As a result of the realization of the axial piston motor as taught by the invention, very small modules can be manufactured. It is also possible, however, to utilize the space made available as a result of the elimination of the stud axle and of the xe2x80x9cinnerxe2x80x9d bearing located on it for a purpose other than a reduction in the size of the cylinder drum.
The space available radially inside the cylinder bores in the cylinder drum, which space is required in the known axial piston motor for the stud axle and the bearings and therefore results in a specified minimum size of the axial piston motor, can be used, for example, for the installation of a device to compensate the engine forces (axial forces) of the axial piston motor. Such a device is described in the above referenced DE 196 42 022 A1, which is herein incorporated by reference. Because such a device, in itself, requires significantly less space than a stud axle to absorb the wheel loads, the cylinder drum can therefore be made smaller.
As long as the engine forces do not exceed certain levels, it is significantly more advantageous, however, if the bearings are realized so that they can absorb both the external forces (wheel loads) and the engine forces. In that case, it is no longer necessary to have a compensation device for the engine forces.
In one particularly advantageous embodiment of the invention, a swash plate is located and oriented so that under operating conditions, the radial components of the engine forces are directed substantially opposite to the wheel loads. The bearings are consequently relieved of the wheel loads. There is a reduction of the bearing load caused by the vertical forces, as a result of which the useful life of the bearings can be increased significantly. The bearings may be made of two tapered roller bearings in an O-layout, in particular conical roller bearings.
The axial piston motor of the invention can be configured both with a constant absorption volume and with a variable absorption volume.
In one layout that has advantages in terms of fabrication, a swash plate in the form of an annular disc is coupled so that it rotates in synchronization with the cylinder drum, is in contact against the control surface of the axial piston motor, and is provided with passage openings to connect cylinder bores of the cylinder drum with hydraulic connections of the axial piston motor.
In another particularly advantageous embodiment of the invention, the swash plate has a bearing surface to support reciprocating pistons. The bearing surface is provided with a concave curvature, and in particular a spherical curvature. As a result of such a shape of the bearing surface, the piston transverse force (radial force) that acts on the reciprocating piston that is extended farthest out of its cylinder bore and is exposed to the operating pressure, which transverse force results from the splitting of forces on the support of the reciprocating piston on the bearing surface of the swash plate, is determined not only by the tilt angle of the swash plate but also by the curvature of the bearing surface. The result, taking into consideration the curvature of the bearing surface, is that the support angle of the reciprocating piston on the bearing surface of the swash plate is smaller than the tilt angle of the swash plate.
Consequently, with the same tilt angle of the swash plate as in the known motor, the piston transverse force of the reciprocating piston that is extended farthest from its bore is reduced. This situation can be used to advantage so that at the same maximum allowable piston transverse force, i.e. taking advantage of the maximum allowable material loads, the tilt angle of the swash plate can be increased, and thus the output of the axial piston motor of the invention can be significantly increased.
The curvature of the bearing surface is appropriately designed so that the surface pressures of the reciprocating pistons in the cylinder bores and/or the deflections of the reciprocating pistons that occur during operation preferably do not differ from one another by more than about 20%, and more preferably by not more than about 10%. In this manner, there is a substantially uniform loading of all the reciprocating pistons and cylinder bores.
The invention teaches that in a particularly advantageous axial piston motor, the tilt angle of the swash plate is preferably between about 20xc2x0 and 30xc2x0 . Such an axial piston motor has small outside dimensions and a large geometric volume flow, and thus a high output capacity. On account of the curvature of the bearing surface of the invention, however, the loads on the reciprocating pistons and cylinder bores are nevertheless not greater than those of engines of the prior art.
In terms of fabrication technology, it is favorable if the control surface is located on a control slide. The control slide can thus be manufactured separately, which facilitates the introduction of the control slots. The swash plate and the control slide are advantageously located on an inclined stud formed on the support part. A spring force is applied to them with the interposition of an axial bearing.
In one advantageous refinement of the invention, a brake is located between the support part and the output part. This brake is preferably a hydraulically releasable spring-loaded brake.
When the axial piston motor of the invention is used as a wheel drive mechanism, it is favorable if the cylinder drum is provided with a wheel fastening flange and a rim centering.